1. Field of the Invention
This invention relates generally to a method for the control of oil and gas production wells. More particularly, it relates to an optical position sensor system for determining the position of movable elements in well production equipment.
2. Description of the Related Art
The control of oil and gas production wells constitutes an on-going concern of the petroleum industry due, in part, to the enormous monetary expense involved as well as the risks associated with environmental and safety issues.
Production well control has become particularly important and more complex in view of the industry wide recognition that wells having multiple branches (i.e., multilateral wells) will be increasingly important and commonplace. Such multilateral wells include discrete production zones which produce fluid in either common or discrete production tubing. In either case, there is a need for controlling zone production, isolating specific zones and otherwise monitoring each zone in a particular well. Flow control devices such as sliding sleeve valves, packers, downhole safety valves, downhole chokes, and downhole tool stop systems are commonly used to control flow between the production tubing and the casing annulus. Such devices are used for zonal isolation, selective production, flow shut-off, commingling production, and transient testing.
These tools are typically actuated by hydraulic systems or electric motors driving a member axially with respect to a tool housing. Hydraulic actuation can be implemented with a shifting tool lowered into the tool on a wireline or by running hydraulic lines from the surface to the downhole tool. Electric motor driven actuators may be used in intelligent completion systems controlled from the surface or using downhole controllers.
The surface controllers are often hardwired to downhole sensors which transmit information to the surface such as pressure, temperature and flow. With multiple production zones intermingled in the single well bore, it is difficult to determine the operation and performance of individual downhole tools from surface measurements alone. It is also desirable to know the position of the movable members, such as the sliding sleeve in a sliding sleeve valve, in order to better control the flow from various zones. Originally, sliding sleeves were actuated to either a fully open or fully closed position. Surface controlled hydraulic sliding sleeves such as Baker Oil Tools Product Family H81134 provides variable position control of the sleeve which allows for continuous flow control of the zone of interest. In order to efficiently utilize this control capability, a sensor system is needed to determine the position of the sleeve. Position data is then processed at the surface by the computerized control system and is used for control of the production well. Similar position data will enhance the efficient flow control of the other downhole tools mentioned. In addition, for critical tools, such as downhole safety valves, indication of the position, or setting, of the valve is desired to ensure that the valve is operating properly.
Thus there is a need for a position sensing system which can monitor the operating configuration of downhole tools by measuring the position of a movable member over a large displacement range.